The application of lighting to the automotive industry is well known. The original electric light sources were filament bulbs which offered high luminance from a small source. Improvements in light source design led to halogen type filament bulbs, high intensity discharge (HID) bulbs or high brightness light emitting diodes (LED). These offer improvement in terms of luminance and energy use over preceding filament bulbs. In order to apply these light sources to automotive front lighting and realise the beam spot distributions required by regulatory bodies, such as the United Nations Economic Commission for Europe (UNECE) or Federal Motor Vehicle Safety Standards (FMVSS), for the U.S.A, modification of the output beam to form specific beam spot distributions on the road is necessary. For projector headlights this requires removal of a portion of the light from the projected beam which ultimately forms the beam spot, to create a dipped beam. The dipped beam is necessary to avoid causing glare to oncoming road users. By necessity, the dipped beam also creates a restricted view of the road due to restricted illumination of the same. The removal of light is performed by a shield, which is inserted into the light path thereby causing a reduction in optical efficiency of the projector headlight.
The filament and discharge light sources provide no means for modification of the output from the source. Therefore, a shield is the only method of providing the dipped beam spot distribution pattern. To switch between a dipped beam and a driving beam, the beam pattern that is necessary for better visibility, either two headlights must be provided, one to create the dipped beam and the other to create the driving beam, or a mechanical switching mechanism must be provided. When the driving beam is desired, the mechanical switching mechanism removes the shield from the projected beam profile allowing all light to exit the projector headlight unit unimpeded.
The provision of only a dipped beam distribution, or of only a driving beam distribution, has limitations in terms of road user safety by not providing simultaneous optimal illumination of the road and minimal glare to other road users. This can be improved upon by the addition of an adaptive element to the projected headlight beam. However, all methods of creating an adaptive beam spot from a single projector unit require mechanical moving components within the headlight unit. This has a limitation on cost reduction and reliability of the headlight over the course of its lifetime. Alternative methods of provision of an adaptive beam spot require multiple light source units, which increases the headlight cost, and which also have a large volume, this having implications for pedestrian safety in the event of a collision.
Laser based light sources offer advantage over existing light sources due to the ability to control the emission from the laser diode effectively using optics with a much reduced size, and therefore, weight. This control ability stems from the small emission area and restricted angular distribution of the laser diode. The light emitted from laser diodes is often illuminated onto a fluorescent material to convert from the first wavelength to a second wavelength, which is predominantly white. The light source created is very small and can be used more efficiently with headlight projection optics.
The following background art describes the use of lasers in automotive headlight units:
JP 2011-134619 A (Stanley Electric, 25 Dec. 2009); an illustration of this patent is shown in FIG. 1. This patent discloses the use of a solid state light source 11 which can be scanned across a fluorescent material layer 12 to form a controllable light source, emitting white or coloured light. The scanning is performed by a moveable reflective method 13, for example mirror. The light is then projected by means of an optical system 14, for example a lens.
EP 2,063,170 A2 (Audi AG, 21 Nov. 2007); an illustration of this patent is shown in FIG. 2. The patent discloses the use of a source of light 21, a two dimensional element 22, a means 23 to image the two dimensional element 22 and a scanning reflector 24. The light source 21 may be a laser diode. The reflector 24 is scanned to move the light emitted 25 from the light source 21 across the two dimensional element 22. This creates a projected distribution 26 of the two dimensional element 22 onto the road surface 27. The reflector 24 is scanned faster than the eye can perceive. The two dimensional element 22 may be formed by a fluorescent material.
US 2012/0051074 A1 (Sharp, 31 Aug. 2010); and illustration of this patent is shown in FIG. 3. The patent discloses a headlight 310 comprising a fluorescent member 31 which is irradiated by laser light 32 emitted by a laser generator 34. The laser generator may be comprised of multiple semiconductor laser devices 37. The position of irradiation is changed by an irradiated position changer 33 which alters the direction of the laser light 32. The irradiated position changer 33 may be formed from a collimating lens which can be rotated by an actuator 35. The angle of the irradiated position changer 33 is defined by the angle of steering of the vehicle; this is detected by a steering angle detector 36. The light is transported from the semiconductor laser devices 37 by optical fibres 38. The fibres are bundled together at their light emitting end 39. The role of the irradiated position changer is to collimate the light and steer the direction of the laser light 32. Only one irradiated position 33 changer is disclosed. The position of irradiation on the fluorescent member 31 defines the direction of projection of the light by a light projecting member 311. The output from the laser generator 34 may be altered dependent on position of irradiation of laser light 32 upon the fluorescent member 31. The patent discloses alteration of both the position of irradiation and area of irradiation.
U.S. Pat. No. 7,654,712 B2 (Koito Manufacturing, 28 Jun. 2006); an illustration of this patent is shown in FIG. 4. This patent discloses a lamp module 41 formed from multiple elements formed from a fluorescent substance 42 excited by individual light emission parts 43 to emit white light. The fluorescent emission from the fluorescent substance 42 is collimated by a plurality of micro lenses 44. This light can then be projected by another lens to form a beam spot. This has the capability to form an adaptive beam spot. The level of fine control of the beam spot is defined by the number of laser diodes.
US 2011/0249460 (T. Kushimoto, 13 Apr. 2011) proposes a vehicle headlight having an array of phosphor squares, which are illuminated by light from blue laser sources. Light from a laser source is directed onto the phosphor grid by a mirror. The lasers can be scanned to obtain different illumination patterns. In addition to the illumination provided by the phosphor grid, the headlight also has a further light source such as a projector or reflector headlight.
EP 2447600 (Stanley Electric Co Ltd, 2 May 2012) proposes a lighting unit that may be for a vehicle headlight. It has a phosphor member that is illuminated by light from a laser diode. The phosphor member is mounted for rotation about its axis, and is shaped such that rotating the phosphor member by 90° about its axis will cause the output illumination pattern of the lighting unit to change.